The present invention relates generally to electron-beam welding and more particularly to an apparatus usable in such a welding operation for maintaining the weld joint in alignment during a multipass-welding operation.
Welding workpieces by utilizing an electron gun for directing an electron beam onto a workpiece to provide sufficient localized heat to effect fusing of the workpiece metal has proven to be a very successful welding procedure for many applications. Electron-beam welding operations are achieved in a chamber under partial vacuum. This confinement of the workpiece normally necessitates that the alignment of the electron beam with the weld joint be made by the operator while looking into the chamber through a scaled viewing window. During multipass-welding operations, continuous positioning of the electron beam with the weld joint by either moving the workpiece or the electron beam gun is necessary for producing satisfactory welds. The misdirection of the electron beam onto the workpiece weld joint by as little as a few thousandths of an inch can seriously detract from the quality of the weldment.
A major problem in maintaining the alignment of the electron-beam gun with the weld joint during multipass-welding operations is due to the shrinkage of the workpiece and welds during each pass as caused by thermal cycling of the weld joint together with the melting of the workpiece material contiguous to the weld joint. The use of filler wire reduces but does not eliminate workpiece shrinkage.
As pointed out above, the electron beam is usually maintained in alignment with the weld joint by the operator during multipass-welding operations. Such alignment requires considerable operator skill and is a time-consuming operation which seriously detracts from the efficiency of the welding operation. Recent developments in welding equipment utilizing electron-beam multipass-welding operations with automatically fed filler wire welding material puts an even further burden upon the operator so as to render especially desirable the use of a mechanism capable of accurately aligning the weld joint with the electron beam during multipass-welding operations.